Huge Page Support

Huge Pages

• Huge pages are also known as superpages in FreeBSD, and large pages in Microsoft Windows terminology.

• Newer AMD64 processors can use 1GB pages in long mode.

• Linux has supported huge pages on several architectures since the 2.6 series via the hugetlbfs filesystem.

• Xen Project supports allocating huge pages for guest. The hypervisor itself doesn't use huge pages.

Use huge pages in Xen Project

• Specify the hypervisor boot command line flag `allowsuperpage` (it was called `allowhugepage` before).

• Create the VM with option `superpages = 1`.

 Note:

 1. This option is for PV guest only; it has no effect to HVM guest.
 2. With this option, PV guest `memory` and `maxmem` must be 2M aligned. Otherwise the VM cannot be started.

• Specify the Linux boot command line flag `balloon_hugepages`.

• In the guest::

   # echo 20 > /proc/sys/vm/nr_hugepages

   # cat /proc/meminfo
   ...
   AnonHugePages:         0 kB
   HugePages_Total:      20
   HugePages_Free:       20
   HugePages_Rsvd:        0
   HugePages_Surp:        0
   Hugepagesize:       2048 kB
   DirectMap4k:     1056768 kB
   DirectMap2M:           0 kB

Reference

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• Huge Pages: http://en.wikipedia.org/wiki/Page_%28computer_memory%29#Huge_pages
• Linux Huge Pages: http://linux-mm.org/HugePages
• https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt